Workpiece having a laser heat-treated surface formed by a small diameter bore extending in workpiece

ABSTRACT

A workpiece has a surface formed by a circular bore extending in the workpiece body along a bore axis. The bore surface includes a heat-affected zone pattern thereon, produced with a laser light beam. The heat-affected zone pattern can be a variety of patterns including a single helix, overlapping helixes a single annular ring and a plurality of annular rings. The heat-affected zones can have a variety of widths, as measured in relation to the longitudinal bore axis.

BACKGROUND OF THE INVENTION

This invention relates generally to heat treating a workpiece using alaser device, and more particularly to heat treating a surface of aworkpiece, the surface to be heat treated being formed by a smalldiameter bore extending in the workpiece.

The manufacture of tightly toleranced small cylinders, many times withcomplex asymmetric thin-walled cross-sections and abrupt diameterchanges, requiring a hardened ID surface can present formidableproblems. The traditional approach requires the through-hardening orcase hardening of a rough machined steel part via conventional meanssuch as quench and temper, or carburizing, followed by difficult andmulti step finish grinding. This approach is time consuming andexpensive.

The foregoing illustrates limitations known to exist in present devicesand methods for hardening internal surface of small diameter bores.Thus, it is apparent that it would be advantageous to provide analternative directed to overcoming one or more of the limitations setforth above. Accordingly, a suitable alternative is provided includingfeatures more fully disclosed hereinafter.

SUMMARY OF THE INVENTION

In one aspect of the present invention, this is accomplished byproviding a laser heat-treated workpiece including a body having aheat-treated surface formed by a circular bore extending in the bodyalong a longitudinal bore axis; a heat-affected zone pattern on the boresurface, the heat-affected zone produced by a laser light beam; theheat-affected zone pattern forming a helix advancing longitudinally in adirection along the workpiece bore surface, the helix having a pluralityof turns, each turn separated from adjacent turns.

The foregoing and other aspects will become apparent from the followingdetailed description of the invention when considered in conjunctionwith the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a schematic drawing showing a workpiece having a surfaceformed by a small diameter bore therethrough being heated by a laser,according to the invention;

FIG. 2 is schematic, partially cross-sectional view of a laser deviceaccording to the invention, for heating a surface formed by a smalldiameter bore in a workpiece;

FIG. 3 is a schematic flow diagram for applying a coating to a surfaceformed by a small diameter bore in a workpiece prior to heating thesurface according to the invention;

FIG. 4 is a perspective schematic view of a workpiece to be heatedaccording to the invention;

FIG. 5 is a view along A--A of FIG. 4 showing various heat affected zonepatterns achieved according to the invention; and

FIG. 6 is a view similar to FIG. 5 showing additional heat affectedzones achieved according to the invention.

DETAILED DESCRIPTION

FIG. 1 shows a workpiece 1 having a small diameter workpiece bore 3therein forming a workpiece bore internal surface 5 to be heated by alaser beam 7 for a purpose such as hardening or other conventionalheat-treatment purposes. Workpiece 1 is supported in a workpiece holder(not shown), to be described hereinafter. Beam 7 is generated by a laser11 of conventional design. Laser beam 7 passes through a conventionalbeam integrator 13 for the purpose of shaping the beam 7 into apreselected geometric pattern having a preselected beam density. Thechoice of beam size and power density would be affected by factorsincluding material to be heated, wall thickness, degree of heating, andfinal application to be satisfied. We have successfully used a squarepattern, 3/16 inch×3/16 inch, with a density of 57 KW/square inch.

The integrator 13 is a model SI061 optical integrator supplied by SparIndustries, Optics Division, of Lake Havasu, Ariz., and it is describedin U.S. Pat. No. 4,195,913.

Beam 7 passes through a conventional lens 15 for the purpose of focusingthe beam 7, as is well known.

Thereafter, beam 7 moves along longitudinal axis 17 of workpiece bore 3and enters workpiece bore 3 to strike the optic means 19 of thisinvention. Optic means 19 includes a reflective mirror 21 positionedtherein on a support member (not shown ), to be described hereinbelow.Mirror 21 is inclined at an angle, preferably 45°, to workpiece boreaxis 17 to cause beam 7 to strike workpiece internal surface 5 at anarea 25 to be heat-treated. Mirror 21 is a highly polished metallicmolybdenum or tungsten member, to survive the laser beam heat. Workpieceinternal surface 5 is coated with a layer 27 of absorptive material toconvert laser beam 7 into heat energy.

As described hereinbelow, workpiece 1 and workpiece holder 2 are movablein relation to support member 17 and mirror 21 in an axial androtational direction, to permit any portion of surface 5 to be impingedby beam 7.

Now referring to FIG. 2, the device of the invention will be furtherdescribed. Workpiece holder 30 comprises an elongated hollow tube 32having an outer surface 34 and an inner surface 36, the inner surface 36forming an enclosed passageway 38. Workpiece holder 30 extends alongworkpiece holder axis 40 that is coincident with workpiece bore axis 13,and terminates in an open first and second end 42,44, respectively.Workpiece holder inner surface 36 is adapted by shape and dimension tomake substantially continuous contact against an outer surface 46 ofworkpiece 1, when workpiece 1 is positioned in passageway 38 withworkpiece bore axis 13 coincident with workpiece holder axis 40.Workpiece holder passageway 38 and workpiece bore 3 form a continuouspassageway along workpiece holder 30, through workpiece 1 and out firstend 42 of workpiece holder 30.

Workpiece holder 30 is supported for rotation about workpiece holderaxis 40 on a pair of spaced apart pillow block bearings 48. Actuationmeans for moving workpiece holder 30 includes a conventional combinationof a motor and drive belt 50. Additionally, workpiece holder 30 is fixedto a table 52 that is movable back and forth parallel to workpieceholder axis 40 by motor 54. Simultaneous control of motors 50,54 isachieved with a conventional, numerically controlled computer device 56,as described more fully hereinbelow.

The optic means 19 includes the mirror 21 positioned in workpiece bore 3spaced from workpiece bore internal surface 5 on a support memberpositioned in workpiece bore 3. The support member is an elongated,hollow stalk 60 having a first end 62 adapted to threadably receivemirror 21, and a second end 64 anchored on a fixed support member 66outside of workpiece holder 30.

Cooling means for cooling the optic means 19 will now be described.Stalk 60 includes a stalk bore 68 with an internal stalk bore surface 70forming an enclosed stalk passageway 72 that extends longitudinallyalong stalk bore axis 74 and terminates in first end 62 and second end64. An elongated, hollow fluid inlet tube 80 extends longitudinallyalong stalk passageway 72 and terminates in an open end 82 adjacent tomirror 21 on first stalk end 62. Tube 80 forms a first passageway forcarrying cooling fluid to mirror 21. Stalk bore internal surface 70 andexternal surface 84 of tube 80 form a second passageway for carryingfluid out of stalk bore 68 via second stalk end 64. Cooling fluid can berecirculated by conventional means (not shown) such as a pump and fluidstorage tank, or used once and discharged.

Additional means for cooling the workpiece 1 will now be described. Afirst jacket 90 is positioned surrounding external surface 34 ofworkpiece holder 30, adjacent first end 42 thereof. First jacket 90 is ahollow housing 92 having a pair of spaced-apart sidewalls 94 extendingradially outwardly with respect to workpiece external surface 34.Sidewalls 94 are positioned in close proximity to each other (preferably4 inches apart). A cross member 96 connects sidewalls 94, whereby jacket90 forms a U-shaped annular container defining three sides of anintermediate space 98 through which a cooling fluid (preferably water)flows. Intermediate space 98 contacts and is bounded by external surface34 of workpiece holder 30. Each sidewall 94 is in sliding contact withexternal workpiece holder external surface 34, whereby workpiece holder30 can rotate with respect to first jacket 90, which is independentlysupported by a support member (not shown). Seals 100 between eachsidewall 94 and workpiece holder external surface 34 retain fluid inhousing 92. Alternatively, first jacket 90 and sidewalls 94 could befixed to workpiece holder 30 and rotate therewith, eliminating the needfor seals 100. Entry port means 102 permits entry of fluid, and exitport means 104 permits exit of fluid. Cooling fluid can be recirculatedby conventional means (not shown) such as a pump and fluid storage tank,or used once and discharged.

For high temperature applications, such as nitriding or carburizing, agas shielding means must be provided to protect the surface area beingheated from contamination and to reduce splatter of molten material. Thegas shielding means will now be described. A second jacket 110 ispositioned on external surface 34 of workpiece holder 30, adjacentsecond end 44 thereof. Second jacket 110 is a hollow housing 112 havinga pair of spaced-apart sidewalls 114 extending radially outwardly withrespect to workpiece external surface 34. Sidewalls 114 positioned inclose proximity to each other (preferably about 2 inches apart). Across- member 116 connects sidewalls 114, whereby jacket 110 forms aU-shaped annular housing 112 defining three sides of an intermediatespace 118 through which a shielding gas flows. Intermediate space 118contacts and is bounded by external surface 34 of workpiece holder 30.Each sidewall 94 is in sliding contact with workpiece holder externalsurface 34, whereby workpiece holder 30 can rotate with respect tosecond jacket 110, which is independently supported by a support member(not shown). Seals 120 between each sidewall 114 and workpiece holderexternal surface 34 retain gas in housing 112. Alternatively, secondjacket 110 and sidewalls 114 could be fixed to workpiece holder 30 androtate therewith, eliminating the need for seals 120. Entry port means122 permits entry of shielding gas under positive pressure intointermediate space 118, and aperture means 124 connects intermediatespace 118 with workpiece holder internal passageway 38. Blocking means126 closes off second end 44 of workpiece holder 30 to prevent shieldinggas from exiting therethrough. A conventional vacuum suction means 128,such as a vented hood, is positioned adjacent first end 42 of workpieceholder 30 to draw vapors or smoke and debris caused by heatinglongitudinally through workpiece holder passageway 38, across area 25being heated and out first end 42, along with shielding gas. Shieldinggas can be selected from the group consisting essentially of argon,neon, xenon, helium and nitrogen, depending in large part upon the typeof heating process to be achieved.

Reflection of laser beam light can occur during operation, resulting inpassage of light along workpiece holder internal passageway 38 towardsecond end 44 of workpiece holder 30. To prevent this condition, laserlight stop means are inserted in workpiece internal passageway 38longitudinally positioned between mirror 21 and blocking means 126.Laser light stop means includes a plurality of spaced-apart annulargraphite plugs 130, in close proximity to each other (preferably 1/4 to1/2 inch). Plugs 130 are positioned in workpiece internal passageway 38transverse to workpiece holder axis 40. Each plug 130 has a plug borehaving a longitudinal plug bore axis coincident with workpiece holderbore axis 40 and an annular outer plug perimeter surface. Each plug boreis connected to stalk 60, with outer perimeter surface slidably incontact against inner surface 38 of workpiece holder 30. Plugs 130completely close workpiece holder passageway 38 surrounding stalk 60.Each plug 130 has a plurality of apertures 134 extending longitudinallytherethrough to permit passage of shielding gas. Each aperture 134 ofone plug 130 is offset, radially or axially, with respect to anyaperture 134 in an adjacent plug, to prevent an aligned passageway forpassage of light beams, while permitting flow of shielding gas.

The actuation means for longitudinally moving workpiece holder 30, withworkpiece 1 therein, will now be further described. A plurality ofspaced-apart support bearings 140 are positioned in workpiece holderpassageway 38 transverse to workpiece holder bore axis 40. Each bearing140 has a bearing bore with a longitudinal axis coincident withworkpiece holder bore axis 40. Each bearing 140 is attached to stalk 60at its bearing bore. Each bearing 140 has an annular outer perimetersurface slidably in contact against inner surface 36 of workpiece holder30. Workpiece holder 30 is longitudinally slidable and rotatable withrespect to stalk 60. Alternatively, bearings 140 can have their outersurface fixed to workpiece holder internal surface 36 and their bearingbores slidable along stalk 60. Also, one bearing 140 can also serve as ablocking member 126 in the shielding gas shield means describedhereinabove. A plurality of apertures 141 in bearing 140 (excluding abearing 140 used as a blocking member 126) permits passage of shieldinggas. Thus, it can be understood that workpiece holder 30 and workpiece 1therein are movable longitudinally and rotationally with respect tomirror 21.

Prior to heating a surface with a laser, it is conventional practice tocoat the surface with an absorptive material that can convert the laserbeam into heat energy to heat the surface. FIG. 4 shows a preferredmethod of coating workpiece internal bore surface 5 of workpiece 1,prior to laser heating. Workpiece bore surface 5 is cleaned, preferablyin a conventional ultrasonic cleaning device, to provide a surface thatwill accept a coating. The surface 5 is heated in ambient atmosphere ina furnace to about 185° F. for about 1 hour to remove moisture. Next,surface 5 is air cooled and thereafter dipped into a liquid carrier,preferably isopropanol, having dispersed herein finely ground absorptiveparticles, preferably graphite. The coated surface is drip dried andheated again in ambient atmosphere to about 185° F. for about 5 minutesto evaporate the carrier liquid, leaving a coating 27 on surface 5. Ifany portions of surface 5 are not covered, steps are repeated, includingdipping, drip drying and reheating, until coating 27 completely coverssurface 5.

We prefer to provide control means 56 as conventional numerical computercontrolled apparatus supplied by Aerotech, Incorporated, sold under theregistered trademark "UNIDEX", model number 16 or model number 21. Usingthe operations available with the control device 56, we havesuccessfully created various patterns of heat-affected zones on theinternal bore surface 5 of small diameter bore 3. FIG. 4 illustrates atypical workpiece 1 having a small diameter (3/4 inch) bore 3 thereindefining surface 5 to be laser heated. FIG. 5 shows a variety of heataffected zone patterns successfully heated according to the invention. Ahelix advancing in a first direction along workpiece bore surface 5, hasa plurality of turns 150, each turn 150 separated from adjacent turns150. The spacing (or pitch) between turns 150 can be varied to anylongitudinal dimension, down to and including zero, in which case theindividual turns 150 overlap to form a continuous stretch forming anannular ring. Also, at least one additional helix advancing in a seconddirection along bore surface 5, second direction being opposite to firstdirection of first helix can be superimposed over the first helix. Theturns 152 of the additional helix can be spaced apart as described forrings 150 of the first helix. Also, one or a plurality of annular,spaced-apart rings 154 (FIG. 6) can be provided.

We prefer the following type of laser: A 5 kW, CO2, continuous wavelaser, with an output at 10.6 microns wavelength, such as provided bySpectra Physics, Inc., Model No. 975. Other lasers that can be usedinclude a continuous wave YAG laser; and a pulsed CO2, YAG or excimerlaser.

We prefer to operate the laser in the power range of 1.9 KW to 2.2 KW.The laser beam is focused on the surface of the substrate by a 10 inchfocal length mirror 21, to cause localized heating melting of thesurface 5. By varying the laser power, and speed of movement ofworkpiece 1, we can vary the temperature attained up to and includingmelting of heated area 25.

We have successfully used the invention to produce a workpiece with ahardened small ID bore having a bore under 3/4 inch diameter, wallthickness of under 1/10 inch, the bore being asymmetrically machinedthrough with abrupt diameter changes and through slots along the borelength. In conventional production techniques, the asymmetrical geometrycaused significant distortion, requiring extensive post-heat-treatmentgrinding and machining. The laser technique of the invention appliedminimum heat only to the surface 5 of bore 3, inducing so littledimensional change, that no further machining was required.

While we have shown a bore 3 extending completely through the thicknessof a workpiece 1, a bore extending part way through the workpiece couldbe heated by providing a U-shaped stalk that entered and exited the sameopening in a bore. Another alternative would be to provide a stalkentering the bore opening, with the stalk having with one passageway forcooling fluid and another passageway for a laser beam, with a mirror atthe end of the second passageway to deflect the beam against the surfaceto be heated. Shrouding gas could be also be introduced into the borevia the stalk.

having described the invention, what is claimed is:
 1. A laserheat-treated workpiece comprising;a. a body having a circular boreextending through said body along a longitudinal bore axis, said borehaving a surface, said surface being heat-treated; b. a heat-affectedzone pattern on said bore surface said heat-affected zone patternproduced by a laser light beam; c. said heat-affected zone patternforming a first helix advancing longitudinally in a first directionalong said bore surface, said first helix having a plurality of turns,each turn separated from adjacent turns; and d. at least one additionalheat-affected zone pattern forming at least one additional helixadvancing longitudinally in a second direction along said workpiece boresurface, said second direction being opposite to said first direction,said at least one additional helix having a plurality of turns, eachturn separated from adjacent turns, said at least one additional helixturns overlapping in cross-wise pattern said turns of said first helix.2. A laser heat-treated workpiece comprising:a. a body having a circularbore extending through said body along a longitudinal bore axis, saidbore having a surface, said surface being heat-treated; b. aheat-affected zone pattern on said bore surface said heat-affected zonepattern produced by a laser light beam; and c. said heat-affected zonepattern forming a plurality of helixes advancing longitudinally alongsaid bore surface, each said helix having a plurality of turns, eachsaid turn separated from adjacent turns, said plurality of helixesoverlapping in cross-wise pattern.